Is there any doubt Apple (Nasdaq: AAPL) will crush earnings expectations later today? There shouldn't be. Apple's made a habit of tearing apart the estimates Wall Street sets for it, and this quarter shouldn't be any different. That doesn't mean Apple's guaranteed to skyrocket tomorrow, though, since expectations tend to build beyond published estimates. Yet Apple's ability to top expectations is still nothing short of extraordinary.

Building optimism
On Friday, on the heels of great earnings from Google (Nasdaq: GOOG) that lifted the tech sector and rising optimism around earnings (one analyst raised his price target on Apple to $500!), Apple soared 4%. To put that in perspective, the amount of value Apple added on Friday alone was equal to half the market value of Yahoo!. Or put another way, in less than two months, Apple has gained more value than key rivals Research In Motion (Nasdaq: RIMM) and Nokia (NYSE: NOK) are worth -- combined.

What's everyone so excited about? For starters, there's anticipation Apple could see its first-ever $20 billion quarter. How could Apple accomplish such a feat? Sales of 13 million iPhones, 9 million iPods, almost 4 million Macs, and around 5 million iPads would get it there.

Those are all amazing figures, and they come in spite of Apple seeing constrained supplies in key products. If Apple didn't have long shipping waits across the quarter, the numbers could be even higher.

Is it too late to buy?
In spite of all the optimism for the quarter, with Apple approaching the $300 billion market-cap barrier, it's worth looking at whether Apple's still an attractive buy. My opinion has been yes. While some people like to point out that Apple can't keep up its string of revolutionary products coming forever, I contend that it doesn't need to.

Its mobile operating system scales extremely well and could form the basis of a more powerful Apple TV product. In addition, further content distribution and ad delivery through Apple's iAd service are both nascent opportunities in Apple's wheelhouse. Throw in continuing growth in smartphones and the iPad besting all expectations set for it, and Apple's value looks reasonable when compared to its growth prospects.

More to watch than Apple
However, if you're leery of investing in Apple at today's level, there's a wealth of other related companies. Key component suppliers like Cirrus Logic (Nasdaq: CRUS) and Broadcom (Nasdaq: BRCM) stand to benefit from Apple posting outsized sales in the coming quarters.

Or if you're concerned about Apple but looking to take advantage of the broader mobile trends, SanDisk (Nasdaq: SNDK), which supplies the Flash memory used as storage in many mobile devices, trades at a reasonable P/E of around 9.

Count on another hit from Mr. Jobs
Apple should be able to ride a wave of iProducts to another record quarter today. I think that's a trend that should play out well beyond today's report, but if you're getting concerned about Apple's run-up, it's a big mobile world out there. Invest accordingly.

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Eric Bleeker owns shares of no companies listed above. Google and Nokia are Motley Fool Inside Value choices. Google is also a Motley Fool Rule Breakers selection. Apple is a Motley Fool Stock Advisor recommendation. The Fool owns shares of Apple and Google. Try any of our Foolish newsletter services free for 30 days. The Motley Fool has a disclosure policy.